Abstract

Although fatty acids (FAs) comprise the components of plant fats and are the main influence on the fat composition of livestock production, their variability during the season is poorly understood. The objective of this research was to quantify FA variation in a northwest Italy alpine grassland over 2 yr. A randomized complete block design was used to study the effect of five harvesting dates per year on FA composition and concentration. The herbage was analyzed for botanical composition, dry matter (DM) yield, neutral detergent fiber (NDF), total nitrogen (TN), and total and individual FAs. Weather data were used to calculate the growing degree days (GDD) and Hargreaves evapotranspiration. The total FA concentration of the herbage decreased throughout the growing season, and was negatively related to the plant age and GDD. The α-linolenic acid (C18:3 n-3), the main precursor of the FAs beneficial to human health present in milk and meat, decreased during the growing stages, and showed a negative relationship with oleic acid (C18:1 n-9) in both the whole herbage samples and in the individual forage species. Drought during 2003 negatively affected the herbage FA concentrations and composition. In general, the greatest C18:3 n-3 forage concentration and the best nutritive value were observed for early spring growth, which suggested that utilization of the sward early in the growing season could provide more FA precursors of milk polyunsaturated FA (PUFA) for animal diets.

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